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Key Features in a Compressor

Hey, I am currently in the design phase of my new compressor. I want to continue my pink noise filter in the control path concept, as well as add a few more filters. Plus I want to add a parallel compression idea to the unit. I was wondering what your thoughts are on these concepts and what other features you might find useful in a compressor. I have a few people interested in selling the Pinky for me, so this next version I really want to make it more appealing to people other than just myself. Thanks!


Rod Gervais Sat, 04/07/2007 - 06:27
I moved this here because it really isn't anything to do with studio construction.

I leve it to the mods here as to whether they conside it spam......... but I didn't think it was seeing as

1. It isn't on the market........

2. it is only inquiring as to the wish list of features from the people in the industry.



Kev Thu, 04/12/2007 - 05:25
EQ and filtering in the sidechain can be very interesting

NON linear functions in the side chain can help make the typical VCA take on some of the aspects of the other topologies in compressors ... and could be a way to emulate tape

I like compressors that give the dynamic reduction and gets the average RMS up BUT without the obvious " I've been compressed sound "
This often does have similarities to tape

We have grown up listening to this type of sound and so it has a easy familiar quality to it

there are times I do like the " I've been compressed sound "
and sometimes even an over compressed feel on aggressive drums.

as with mic-pres ... the more compressor styles I have available ... the happier I am.

choice ... lots of choice is good

How important is propagation delay in multi-band compressors?
digital / plug-in ?
any DSP effect with long latency can be a problem

an analog multi-band doesn't have to have a delay ??
as with many effects ... there can be some phase issues
but the benefits can outweigh these issues

some even like parallel compression

Kev Tue, 04/17/2007 - 00:30
A do it all box is something that people aspire to
but often never reached.

A single or narrow sweet spot box is a good reliable thing that will serve you well for years ... ala LA2 or 1176 etc

a do it all has merit as long as it does in fact do most stuff well.

the one switch DeEsser may not be the way to go
I think it need to sweep ... different voices have a different peak

Think about a hi pass filter.
the low end has the larger amplitudes that can over cook a comp sidechain/detector.
perhaps a choice of 12db or 6dB per oct ... like the synth boys like.

Think about an EQ or Tone slope control instead of the Pink Filter.

A simple Hi Cut at 3dB/oct could be good.

The Multi Band and Phase issues.
I don't think a change in phase is an issue by itself
when the two bands are mixed together the phase issues ARE a problem just as they are with an active crossover.
People like LR filters but that's not the ultimate as the speakers have issues.
It is the amp/speaker combination needs to be LR.
get back on topic Kev !
for compressors the phase of each band needs to coincide when the bands come together.
the same goes for parallel comp.
basically the idea can't work perfectly anyway (yeah, yeah, the geeks will have something to say here)
or you could do what most do
and just ignore it
and say it sounds better so I'll continue to use it.

keep the crossover band very very tight and so the comb filtering will be narrow.
DSP may make it easier to set up a continuously variable rather than 3 or 4 discrete bands ... etc etc

LAST thought ...
BurrBrown Volume control chips (PGA range)
then use a PIC as the side chain.
write different algorithms for the PIC.

definitely my LAST thought
Midi Control ... head for MidiBox and the forum
big project
but do-able

Link555 Thu, 04/12/2007 - 06:08
Hey thanks, Kev. Yep you nailed what I was trying to say;-> By propagation delay I was taking about the time (or phase) change across each section of the filter compared to the straight through parallel path. I am curious if I need to add some all pass filters to the direct path to "delay" or make up for the phase issue. I know when I do the same on the mixer in a mix, it doesn't matter. But if I were ever going to split hairs I would rather do it in the conceptual design phase. No pun intended.J

I agree with you on the tape compression. When I first tried out the pink noise filter idea, I though it might help bass tracking, but it sounds really sweet on vocals. What I am thinking for this compressor is a faceplate full of switches to flip in different filters.

First the basics:
-RMS/PEAK switch
-Hard Knee/Soft Knee switch (I am toying with the idea of pot control for this one)
-A mix style knob to add in original signal to the compressed signal.

Then on/off style switches for the following
-Pink Noise Filter
-Tunable frequency (maybe state variable filter for this)

So thanks again for your input, anything you would add?

Link555 Sat, 04/07/2007 - 11:21
LoL Thanks for the the response
ok sure I won't make anything that sounds like the stock 3630.

Mine however is not a stock 3630. I have changed almost every key component in my modded 3630. It has new VCAs, RMS detectors, a new functional power supply +/-18V rails, and almost all poly caps. TO me,my modded version is a pretty good artifact compressor. But as far as what I have used in the past, lets see:
Cranesong STC, tracker
API 2500
manley variable mu
Drawmer 241, 1960
Weiss DS1
ART Tube Pac
DBX 266
tube tech CL 2A
and A few other I can't think of.

So my question is more what kind of features you personally like in a compressor?

Link555 Tue, 04/17/2007 - 06:52
Thanks Kev!

"Or you could do what most do
And just ignore it
And say it sounds better so I'll continue to use it.
LOL- nice

Yep I agree with the Desser comment, sweepable band or a parametric is what I will use. I might just make up three and sum them together.

Your right on about the summation phase problems though, this is where I going to have slow down and figure things out. But I may opt for "it sounds better" until I do ;)

I might throw in a DSP PIC, I have a sample on my desk at work that’s begging to get used. However I really want to keep the audio path as analog as possible.

I will order some sample of the BB PGA's today, how do they sound?

PGA controlled by a PIC is pretty much what the RNC is all about. (Although I think he controlled a THAT VCA, if I remember correctly.

I think for the next version I will stick with the THAT 4301 audio engine, as I have 24 left.

Wow midi control for a compressor?
Very interesting (taps finger tips together)

Thanks again Kev, great stuff!

Link555 Sat, 04/07/2007 - 13:08
Hey DCJ, Thanks for the response :)

Actually I have built a few versions of the LA-2A for other people. I agree they definitely have their place.

What features of the LA-2A do you like?
Specifically is it the tubes?
The photo resistor?
The Simplified interface?
Do you mind the noise floor issues?

I am trying to get a sense from people what features they like in a compressor.

Like for example would you use a filter section in the control path?

Or do prefer a more transparent compressor with parallel compression used inside?

How important is propagation delay in multi-band compressors?

Stuff like that.

I am just curious what other people like about compressors and their features.

Thanks again!

RemyRAD Sat, 04/07/2007 - 23:39
OK, one of the things I like, is the character of the sound of the compression/limiting. That's paramount. The LA 2 sound was not just the photosensitive resistors and tubes combination. It was its light source. Not a light bulb. Not a LED. But a Electroluminescent Panel and you just don't see those darned things in any other optical compressor/limiter's. Their ballistics and persistence is different from that of any other light source. Then of course comes the photosensitive resistors, which are not your mother's old-fashioned Radio Shaft recipe. Don't get me wrong. Optical is cool when you want optical. Otherwise, give me a nice fast FET that is a "voltage variable resistor" across the input of a good line driver amplifier, like in the old 1176.

Would I like a variable filter in the detector? You mean? Would I like an equalizer built into the side chain? If it served my purposes and if I still had access to the side chain? Sure. I'd definitely use that. Something I've done too many a 1176. I even like the 25, 50 & 75 microsecond preemphasis curves on the high frequency limiter section of my Orban 418A "OptiMod" style limiter. It was particularly handy when making cassettes for customers, in the old days.........

O l d d a z e.......................................old duh

Link555 Sun, 04/08/2007 - 08:46
Hey thanks RemyRAD.

Yes that’s what I mean a built in filter in the side chain. My original concept with pinky was to put an inverse pink noise filter in the control path. Doing make the compressor compress lower frequencies more than upper frequency. It also introduce a few phase distortion, as any EQ in the side chain would. However in the case of the first pinky I like this sound. I was attempting to compress the signal in a way similar to the way the human ear does. But along the way of making the first prototype I started dreaming about adding a built is desser band and others. So thanks for confirming the usefulness of the feature.

Thanks Sebatron,
I like the idea of second compressor in the side chain. That’s something I want to think on for a while. By the way great site, your products look very impressive!

Thanks great answers just what I was hoping for!

Pro Audio Guest Thu, 04/12/2007 - 21:12
okay, i am probably going to get amazingly flamed for this, but Ill say it anyways.

First off, a lot of people like playing with knobs and what not, BUT... dont you hate it when you are tracking a kick drum and you get the most perfect punchy sound, and then, you write down your knob settings or something, and start tracking vox. Then you go back another time and put in the kick drum settings, but you cant get it just right?

I think a digital interface would be really cool, with recall and stuff, WITHOUT any AD/DA. Mesa's triaxis preamp does this, and so does a certain soldano amp. What it does is it has a digital interface or something, which doesnt change the sound at all, but rather control a motorized pot. So the sound and pots are still all analog, but the settings and stuff are digital. It would be awesome.

It would open up a number of features people could use... midi control of the compressor (so people could change the settings of the outboard compressor or sometihng from their daw, or use a footpedal or something like that), and recall of settings.

Thats just my 2 cents... dont flame me :p

Link555 Thu, 04/12/2007 - 21:31
Hey that’s a really cool Idea, I actually did that exact thing on a pre-amp/ Eq unit I built for someone a year or two ago. We used digital pots in the all-analog audio path. I had a Pic microprocessor in there to handle the pot position based on the knob encoders on the front. It had total recall with 255 steps of resolution for each knob. However if I remember correctly it only 2 storage banks, so 2 different setups could be stored, but that could easily expanded in the pinky.

Yep I like that idea a lot, maybe pinky three will have that in it. Thanks man!

Kev Sun, 04/08/2007 - 16:54
You already have a little experience with the THAT VCA in the Alesis 3630 and so some experimenting with a better version of this could be the way to try a few things fast.

see the DINgO from JLM Audio

it's a universal I/O PCB that can be used as balanced and unbalanced in a variety of combinations.
It also takes a 218* VCA IC direct on the PCB for a VCA comp.

Joe already has a couple of front panel side chain combinations both as compressors and EQs.

It can handle more than a few options of amp ... from IC to DOA from a number of the usual suspects
... try the JLM Hybrid.

and you can post questions on Joe's forum.

an un-ashamed plug

Link555 Sun, 04/08/2007 - 18:22
Hey Kev, thanks for the info. And Yes I have used THAT Audio Engine chips in the past. I like them. Currently I have a few PCB's ready for testing with pinky, so trying ideas is super easy. Joes page is impressive and I have stumbled upon both the DIY factory and JLM in the past. Cool stuff.

But actually I am more interested in getting users perspectives on what they find useful. I know what I want in a compressor, but I want to see what other people want.

Pro Audio Guest Fri, 04/13/2007 - 08:21
haha thanks. I honestly thought i was going to be flamed big time.

But yea, I would love to see that in a high end compressor, or any/all pro audio gear. Theres not really any negatives about it, except for maybe the unit wouldnt last as long because the motors would wear out or something of that sort, but imagine...

a fully analog studio, with digital accuracy and recalling and stuff... none of the quality problems involved with A/D/A. That would sick.

ORRRRRR take it to a new level...

and entire DAW and editing system based of this..... all the editing and what not is totally digital.. say in like protools, yet each action you do on the computer just controls a motorized pot for an all analog signal.

who knows.. maybe this is what the future holds.

Weve basically gone from analog to digital..... now lets the best of both worlds and mix em! =D